.button-85 {
  padding: 1em 6.8em;
  border: none;
  outline: none;
  color: rgb(255, 255, 255);
  background: #111;
  cursor: pointer;
  position: fixed; /* Giữ nguyên fixed để nút ở vị trí cố định */
  z-index: 3;
  border-radius: 10px;
  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
  font-family: Arial, sans-serif;
  font-size: 15px;
  font-weight: bold;
  color: #fff;
  text-transform: uppercase;
  bottom: 25px;
  right: 50px;
}

@media (max-width: 768px) {
  .button-85 {
    padding: 0.8em 4em;
    font-size: 14px;
    bottom: 15px;
    left: 50%; /* Căn giữa theo chiều ngang */
    transform: translateX(-50%); /* Dịch chuyển nút về giữa */
    right: auto; /* Loại bỏ giá trị `right` */
  }
}

.button-85:before {
  content: "";
  background: linear-gradient(
    45deg,
    #ff0000,
    #ff7300,
    #fffb00,
    #48ff00,
    #00ffd5,
    #002bff,
    #7a00ff,
    #ff00c8,
    #ff0000
  );
  position: absolute;
  top: -2px;
  left: -2px;
  background-size: 400%;
  z-index: -1;
  filter: blur(5px);
  -webkit-filter: blur(5px);
  width: calc(100% + 4px);
  height: calc(100% + 4px);
  animation: glowing-button-85 20s linear infinite;
  transition: opacity 0.3s ease-in-out;
  border-radius: 10px;
}

@keyframes glowing-button-85 {
  0% {
    background-position: 0 0;
  }
  50% {
    background-position: 400% 0;
  }
  100% {
    background-position: 0 0;
  }
}

.button-85:after {
  z-index: -1;
  content: "";
  position: absolute;
  width: 100%;
  height: 100%;
  background: #222;
  left: 0;
  top: 0;
  border-radius: 10px;
}